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IDAS SYSTEM

IDAS ICOM DIGITAL ADVANCED SYSTEM

IDAS is Icom’s digital land mobile radio system using the NXDN™ common air interface. IDAS offers a complete system of handheld radios, mobile radios, repeaters, network interface/trunking controller, remote communicator, system manager software and various accessories. IDAS is a complete digital solution that system owners or operators can grow into as their time and budgets allow.

IDAS SYSTEM FEATURES

 Spectrum efficiency 

The IDAS system utilizes 6.25kHz narrowband FDMA technology. This system is not only spectrum efficient, but meets the FCC 2013 deadline for narrow band compliance.

 IDAS Trunking 

IDAS trunking conforms with the NXDN™ type-D trunking protocol. IDAS trunking is a distributed system which does not use a dedicated control channel, and is an affordable digital trunking solution for high volume users.

 Audio quality and coverage 

When compared to an analog FM signal, digital easily outperforms analog in audio clarity at the fringes of the communication range, thus providing more reliable audio over a greater total area, even if the coverage footprint is the same as analog FM.

 Flexible IP Network 

IDAS repeater sites* can be interlinked over an IP Network, and can extend your communication coverage. When used with a VE-PG3, VoIP Gateway, the IDAS radios* can be integrated into the SIP and analog phone system and interconnects telephone calls.

* IDAS multi-site trunking and IDAS multi-site conventional mode.

 Secure conversation 

The digital modulation/demodulation makes it difficult to decode the IDAS digital signal using current scanner receivers. The digital voice scrambler adds security on your conversation.

 Flexible migration path 

The IDAS system allows you to scale migration to narrow band digital at your own pace and needs, while running your existing analog system. As your future communication needs change, the IDAS system can grow to a trunking system and/or wide area (multi-site) system.

 

 Source: ICOM

NXDNCOMMON AIR INTERFACE

APPLICATIONS | Technical characteristics | Application functions | AUDIO QUALITY | IDAS Radios

NXDN is a Common Air Interface (CAI) technical protocol for mobile communications. It was developed jointly by Icom Incorporated and Kenwood Corporation.

NXDN is implemented by Icom in their IDAS system [1] and by Kenwood as NEXEDGE;[2] both Kenwood and Icom now offer dual-standard equipment which supports the European dPMR standard.

Applications

The NXDN protocol and the communications products in which it is used are intended for commercial Private Land Mobile Radio (PLMR) [5] and low-end public safety communications systems. The technology satisfies the U.S. Federal Communications Commission (FCC) mandate requiring all communications systems covered by Part 90 regulations to use narrowband technology by 1 Jan 2013. Part 90 regulations specify a bandwidth of 12.5 kHz, but the FCC “strongly urges licensees to consider migrating directly to 6.25 kHz technology rather than first adopting 12.5 kHz technology and later migrating to 6.25 kHz technology.” The FCC “will expeditiously establish a schedule for transition to 6.25 kHz narrowband technology.”

Technical characteristics

NXDN uses Frequency-Division, Multiple-Access (FDMA) technology in which different communication streams are separated by frequency and run concurrently. Time-Division, Multiple-Access (TDMA) systems combine the communications streams into a single stream in which information from the different streams is transmitted in interleaved time allocations or "slots." Code-Division, Multiple-Access (CDMA) systems allow many users to share a common spectrum allocation by using spread-spectrum techniques.

The basic NXDN channel is digital and can be either 12.5 kHz or 6.25 kHz wide. 6.25 kHz dual-channel systems can be configured to fit within a 12.5 kHz channel. This effectively doubles the spectrum efficiency compared to an analog FM system occupying a 12.5 kHz channel. The architecture of NXDN is such that two NXDN channels, within a 12.5 kHz channel for example, can be allocated as voice/voice, voice/data, or data/data. As of 2012, this capability cannot be implemented in commercially available hardware on simplex or "talkaround" frequencies, but only through repeaters.

Systems that use NXDN also support mixed analog FM and digital NXDN equipment, including direct radio-to-radio communications. This allows system owners to migrate to a narrowband, digital system without replacing the entire system at once. NXDN equipment is currently FCC type-accepted for use on VHF (136-174 MHz) and UHF (400-520 MHz) bands.

Data is transmitted using 4-level frequency-shift keying (FSK) modulation. NXDN uses the AMBE+2 vocoder (codec) for digital audio.[7] This combination provides better weak-signal voice quality than for analog FM. For an equivalent transmitter power, NXDN is represented as having a wider range and slightly better multi-path characteristics than analog FM in typical RF environments, specifically at the 12 dB SINAD threshold. The transmission bit rate is 4800 bit/s.

The following FCC emission designators apply to NXDN transmissions:

    8K30F1E 12.5 kHz single channel digital voice
    8K30F1D 12.5 kHz single channel digital data
    8K30F1W 12.5 kHz single channel digital voice and data
    4K00F1E 6.25 kHz single channel digital voice
    4K00F1D 6.25 kHz single channel digital data
    4K00F1W 6.25 kHz single channel digital voice and data
    4K00F2D 6.25 kHz single channel analog CW ID

Application functions

The NXDN protocol provides support for the following functions. Implementation of the functions and the user-level interfaces by which they are accessed and used may vary by manufacturer.

    Encryption – Spectrum-inversion digital voice scrambling with a 15-bit key for 32,768 different codes
    Paging & Status Reporting – Radio-to-Radio and Dispatch-to-Radio
    User Aliases – 65,545 different Group ID's and User ID's
    Man-down and Emergency call
    Remote radio management functions - Stun/Kill/Revive and Monitor
    Over the Air Programming
    Over the Air Alias
    Interface to third party applications for; Paging to radio, GPS Location, Taxi Data Terminals, In Building tracking

Audio quality

In all lossy compression schemes, trade-offs are made in voice reproduction quality in return for minimizing the raw bit rate of the transmission. This leads to artifacts and compromises of frequency response in reproduced speech. Encoders and other compression schemes that are highly-optimized for speech are often unsuitable for non-speech audio, such as music or frequency-shift keyed data. Using an inappropriate encoder usually results in the creation of distortion and artifacts in the reproduced audio.

The audio reproduction quality of IDAS and NEXEDGE communications systems is dependent on the performance of the AMBE+2 voice codec used by NXDN. The AMBE family of vocoders has been subjected to comparative testing and found to be adequate for its intended uses, primarily mobile and aeronautical radio. The AMBE+2 vocoder has also been selected for use in the Motorola MOTOTRBO radio family and the Project 25 (P25) mobile radio system. The following reports and papers are descriptions of laboratory-environment evaluations of AMBE+2 and other speech vocoders.

Compromises in audio quality are inherent in the use of any codebook-based speech coder, particularly when used in conditions of high background noise. Incremental improvements are being made in the algorithms, which may lead to differences in performance even while the basic method remains unchanged. In the US, the Department of Commerce Public Safety Communications Research laboratory regularly reports on progress in this field. While their work specifically pertains to Project 25 radios, it is directly applicable to any system using similar multi-band excitation coders.

Source: wikipedia.com

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